1,3-butadiene can be a valuable petrochemical product. It is a simple conjugated diene and can be a useful monomer in the production of synthetic rubber, adiponitrile, and chloroprene, among other materials. It also can be used in the Diels-Alder reaction to produce cycloalkanes and cycloalkenes.
1,3-butadiene is a component in C4 hydrocarbon streams produced by cracking processes, e.g., steam cracking of naphtha, gas cracking, and catalytic cracking of gas oil and/or vacuum gas oil. C4 hydrocarbon fractions are separated from lighter and heavier hydrocarbons using a fractional distillation column, such as a debutanizer. C4 hydrocarbon streams can include butane, isobutane, isobutene, 1-butene, trans-2-butene, cis-2-butene, 1,3-butadiene, 1,2-butadiene, methylacetylene, ethylacetylene, vinylacetylene, and/or other components. It can be desirable to further isolate 1,3-butadiene from other components to produce a purified 1,3-butadiene stream.
Because 1,3-butadiene has low relative volatility compared to other components in a C4 hydrocarbon stream, it is often separated using extractive distillation. Thus, purification of 1,3-butadiene from C4 hydrocarbons can be carried out in two stages of extractive distillation: (1) to separate butanes and butenes to produce crude butadiene; and (2) to separate vinyl- and ethyl-acetylenes from crude butadiene. Extractive distillation may be followed by conventional distillation to remove methylacetylene. Because of the large amounts of solvent involved in extractive distillation, this process can be highly energy intensive. Further, separated acetylenes are often sent to a flare, and because of risk of explosion, must be diluted with valuable 1,3-butadiene.
Certain methods of purifying 1,3-butadiene are known in the art. U.S. Pat. No. 2,847,487 discloses a pre-wash containing cuprous ammonium acetate solution to form copper acetylides from acetylenes in crude butadiene. U.S. Pat. No. 2,963,523 discloses a pre-wash system including the recovery of butadiene from the pre-wash solvent by desorption. U.S. Pat. No. 3,898,298 discloses a method of selectively hydrogenating vinylacetylenes in a crude butadiene stream by reaction with hydrogen in the presence of a palladium and aluminum catalyst.
There is an interest in alternative methods of purifying 1,3-butadiene. One technique uses “click chemistry,” a term sometimes applied to reactions that have high yield and produce products that are easily separated. An azide-alkyne cycloaddition reaction is a simple reaction that can be employed to remove acetylenes from 1,3-butadiene. In the azide-alkyne cycloaddition reaction, an organic azide reacts with acetylenes to form a triazole. For example, U.S. Pat. No. 7,275,234 discloses a method of forming cycloaddition triazoles from organic azides and terminal acetylenes in the presence of a catalyst.
There remains a need for improved methods of purifying 1,3-butadiene from a C4 hydrocarbon stream.